thanks for all your answers but well i went on Nvidia website and it says that GTX 560 ti SLI is 66 FPS average,with 660 ti ,its 62 FPS average and well,if i overclock the cards, i can get even better FPS,finally the power consumption is not enormous,ill prolly be able to overclock

and well ill buy a cheap GTX 560 ti , 160 euros,means that will be 380 euros for both cards and better FPS,i think its quite the same performance per dollar so well ill have more noise i know but i think ill have the 560 ti SLI,thanks for your help ;)